Data converter having a passive filter

ABSTRACT

Exemplary implementations of electrical circuits and systems are disclosed, and methods for signal processing including sampling and quantizing of amplitude and band limited signals implemented through a Passive Pulse Modulation Analog to Digital Converter (PMADC).

RELATED APPLICATIONS

This application is a Continuation application of U.S. application Ser.No. 12/615,994, which was filed on Nov. 10, 2009. The entire contents ofthe U.S. application Ser. No. 12/615,994 are hereby incorporated hereinby reference.

BACKGROUND

It is often a goal of electronic designers to design circuits thatutilize a low supply voltage and/or consume a minimum amount of power.This may particularly be the case for Analog to Digital Converters(ADC).

Various known techniques may reduce the high power consumption common tomany ADC devices. Such techniques include a Pulse Modulation ADC usingirregular sampling, as disclosed in United States Patent Application US2009/0091486 A1, to Wiesbauer et al., which is incorporated herein inits entirety.

A contemporary Pulse Modulation ADC converts a continuous time analogsignal into a discrete time digital signal. The Pulse Modulation ADC isprimarily composed of a modulator and a measurement engine, andgenerally includes a demodulator or other digital signal processor. TheSigma-Delta configuration of the modulator of the contemporary PulseModulation ADC is characterized by the inclusion of active elements.Specifically, the modulator of the Pulse Modulation ADC generallyincludes an operational amplifier or operational transconductanceamplifier acting as an integrator.

As the frequency of operation increases, the behavior of the activeintegrator becomes less ideal, and so the benefit (the linear response)of using an active element such as an operational amplifier in asummation function is generally lost, and the disadvantages to using theactive element (increase in size and power consumption to maintainacceptable performance characteristics) become more apparent. Therefore,the Pulse Modulation ADC may still require a higher than desired supplyvoltage, and consume relatively more power, in addition to requiringgreater circuit area. Any increase in the consumption of power andcircuit area is usually not desirable, especially in implementationsperformed with 100 nm technology or smaller.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical items.

FIG. 1 is an exemplary environment in which techniques in accordancewith the present disclosure may be implemented.

FIG. 2 illustrates an exemplary implementation of a Passive PulseModulation Analog to Digital Converter (PPMADC).

FIG. 3 illustrates an exemplary PPMADC.

FIG. 4 illustrates a differential implementation of an exemplary PPMADC.

FIG. 5 illustrates a circuit diagram of the modulator stage of thePPMADC shown in FIG. 4.

FIG. 6 illustrates a flow diagram for implementing analog to digitalconversion using an exemplary PPMADC circuit.

FIG. 7 illustrates an electronic device implementing a Passive PulseModulated Analog to Digital Converter using irregular sampling.

DETAILED DESCRIPTION

Exemplary implementations of passive electrical circuits and systems aredisclosed describing a high-resolution, high bandwidth streaming ADCthat is based on time-domain resolution. Implementations are explainedin more detail below using a plurality of examples. Although variousimplementations and examples are discussed here and below, furtherimplementations and examples may be possible by combining the featuresand elements of individual ones.

Exemplary Systems

FIG. 1 illustrates an exemplary environment 100 in which techniques inaccordance with the present disclosure may be implemented. In thisimplementation, the environment 100 includes a communication device 110,or other mobile and/or electronic device, having one or more analog todigital converter circuits 150 configured in accordance with theteachings of the present disclosure. The communication device 110operatively communicates via one or more networks 140, such as wirelesslocal area network (WLAN), with a plurality of other devices 142.Alternatively, the communication device 110 may bypass the networks 140and communicate directly with one or more of the other devices 142.Detailed descriptions of various aspects of analog to digital convertercircuits, methods, and techniques are provided in the following sectionswith reference to FIGS. 2 through 7.

In the representative environment 100, the communication device 110 is ahand-held device, such as an MP3 (Moving Picture Exerts Group Layer-3)player, a personal data assistant (PDA), a global positioning system(GPS) unit, mobile telephone, smartphone, or other similar hand-helddevice, and the other devices 142 may include, for example, a computer142A, another hand-held device 142B, a compact disc (CD) or digitalvideo disc (DVD) player 142C, a signal processor 142D (e.g., radio,navigational unit, television, etc.), and a mobile phone 142E. Inalternative implementations, of course, the devices 110, 142 may includeany other suitable devices, and it is understood that any of theplurality of devices 142 may be equipped with analog to digitalconverter circuits 150 that operate in accordance with the teachings ofthe present disclosure.

As further shown in FIG. 1, the communication device 110 includes one ormore processors 112 and one or more communication components 114, suchas input/output (I/O) devices (e.g., transceivers, transmitters,receivers, etc.), coupled to a system memory 120 by a bus 116. In theimplementation shown in FIG. 1, the analog to digital converter circuit150 is included as a component within the communication component 114 ofthe communication device 110. In alternative implementations, however,the analog to digital converter circuit 150 may be integrated with anyother suitable portion of the device 110, or may be a separate,individual component of the device 110.

The system bus 116 of the communication device 110 represents any of theseveral types of bus structures, including a memory bus or memorycontroller, a peripheral bus, an accelerated graphics port, and aprocessor or local bus using any of a variety of bus architectures. Thecommunication component 114 may be configured to operatively communicatewith one or more external networks 140, such as a cellular telephonenetwork, a satellite network, an information network (e.g., Internet,intranet, cellular network, cable network, fiber optic network, LAN,WAN, etc.), an infrared or radio wave communication network, or anyother suitable network.

The system memory 120 may include computer-readable media configured tostore data and/or program modules for implementing the techniquesdisclosed herein that are immediately accessible to and/or presentlyoperated on by the processor 112. For example, the system memory 120 mayalso store a basic input/output system (BIOS) 122, an operating system124, one or more application programs 126, and program data 128 that canbe accessed by the processor 112 for performing various tasks desired bya user of the communication device 110.

Moreover, the computer-readable media included in the system memory 120can be any available media that can be accessed by the device 110,including computer storage media and communication media. Computerstorage media may include volatile and nonvolatile media, removable andnon-removable media implemented in any method or technology for storageof information such as computer-readable instructions, data structures,program modules, or other data. Computer storage media includes, but isnot limited to, random access memory (RAM), read only memory (ROM),electrically erasable programmable ROM (EEPROM), flash memory or othermemory technology, compact disk ROM (CD-ROM), digital versatile disks(DVD) or other optical disk storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium, including paper, punch cards and the like, which can be used tostore the desired information and which can be accessed by thecommunication device 110.

Similarly, communication media typically embodies computer-readableinstructions, data structures, program modules or other data in amodulated data signal such as a carrier wave or other transportmechanism and includes any information delivery media. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection and wireless media such as acoustic, RF, infrared and otherwireless media. Combinations of any of the above should also be includedwithin the scope of computer readable media.

Generally, program modules executed on the device 110 (FIG. 1) mayinclude routines, programs, objects, components, data structures, etc.,for performing particular tasks or implementing particular abstract datatypes. These program modules and the like may be executed as a nativecode or may be downloaded and executed such as in a virtual machine orother just-in-time compilation execution environments. Typically, thefunctionality of the program modules may be combined or distributed asdesired in various implementations.

Although the exemplary environment 100 is shown as in FIG. 1 as acommunication network, this implementation is meant to serve only as anon-limiting example of a suitable environment for use of the analog todigital converter circuit 150 in accordance with present disclosure.Similarly, the device 110 is simply one non-limiting example of asuitable device that may include analog to digital converter circuits150 in accordance with the present disclosure.

Exemplary Passive PMADC Implementations

FIG. 2 illustrates an exemplary implementation of a Passive PulseModulated Analog to Digital Converter (PPMADC) 200. It is to beunderstood that the PPMADC 200 may be implemented as, or part of anothersystem such as a TV tuner card, mobile communications systems, Bluetoothtransmission systems, Very high speed Digital Subscriber Line (VDSL)systems, and the like. Because of its lower power consumption and arearequirements due to the use of primarily passive elements (an activeintegrator is not included in the circuit), a PPMADC 200 may beimplemented successfully in 100 nm or less technology operating at highfrequencies (for example, hundreds of megahertz). In an exemplaryembodiment, the PPMADC 200 is composed of a first stage comprising ananalog modulator 202, and a second stage comprising a Measurement Engine204.

Modulator

The modulator 202 converts an input analog signal into a correspondingpulse modulated digital signal using time-discrete irregular sampling ofthe input signal. The modulator 202 can convert the magnitude (forexample amplitude information) of the input analog signal into timeinformation in time domain. This is commonly referred to as PulseModulation (PM) or duty cycle modulation. The amplitude of the inputsignal may be converted into time encoded information in theinstantaneous frequency and/or the duty cycle of a square wave by themodulator 202. For example, given low amplitudes of the input analogsignal, the duty cycle of the output square wave may be low, and givenhigh amplitudes of the input analog signal, the duty cycle of the outputsquare wave may be high.

In an embodiment, the modulator 202 generates an asynchronous squarewave with a duty cycle that is linearly dependent on the input analogsignal. In addition, the modulator 202 can generate an instantaneousfrequency, which is non-linearly dependent on the input analog signal.The modulator 202, in an exemplary asynchronous embodiment, may beimplemented without any clock and can be operated at low currents andsupply voltages. Further, as an advantage to asynchronous operation, theoutput signal of the modulator 202 may avoid errors introduced byquantization. Thus, the output signal of the modulator 202 is a betterrepresentation of the input analog signal.

In an exemplary embodiment, the modulator 202 includes a passivecontinuous time filter 220 and a comparator 222. The passive continuoustime filter 220 may generally have two inputs, a first input 224receiving an analog signal that is an input signal to the PPMADC circuit200, and a second input 226 receiving a feedback signal. The passivecontinuous time filter 220 filters the input analog signal and thefeedback signal, and also combines the signals received at the first andsecond inputs. The combined signal comprising the analog input receivedat the first input 224 and the feedback signal received at the secondinput 226 is the output signal of the passive continuous time filter 220and the input signal to the comparator 222. In one embodiment, no otherelements are in the signal path between the output 228 of the passivecontinuous time filter 220 and the input 230 to the comparator 222. Inan alternate embodiment, an additional passive filter 232 is added tothe signal path between the output 228 of the passive continuous timefilter 220 and the input 230 to the comparator 222, providing additionalfiltering to the output signal of the passive continuous time filter220.

It is advantageous to have a purely passive signal path from the inputof the passive filter 220 to the input of the comparator 222. Thebenefits include lower power consumption by the circuit, less physicalcircuit area required, the ability to scale the circuit to smallerimplementations (e.g., 100 nm or less technology), higher speed andbandwidth capabilities (e.g., hundreds of MHz), minimum voltage domainsignal processing, high resolution, improved streaming capability, andthe like. In exemplary embodiments of the PPMADC circuit 200, no activeelement is present in the signal path between the inputs 224 and 226 ofthe passive continuous time filter 220 and the input 230 to thecomparator 222.

In an exemplary embodiment, the comparator 222 is the only activeelement of the first stage of the PPMADC 200. Additionally, thecomparator 222 is usually asynchronous. The comparator 222 compares theoutput signal of the passive continuous time filter 220 with at leastone reference voltage to produce an output signal. In general, acomparator, such as comparator 222, compares two input voltages orcurrents and switches its output to indicate which of the two inputs islarger. In this example, one of the signals received by the comparator222 may be a reference voltage. In an embodiment, the combined signalreceived from the passive continuous time filter 220 is compared with areference voltage by the comparator 222. The reference voltage may be apredefined value.

In an embodiment, the output signal from the comparator 222 can switchfrom low to high if the output signal from the passive continuous timefilter 220 rises above the reference voltage. In another case, theoutput signal from the comparator 222 can switch from high to low if theoutput signal from the passive continuous time filter 220 drops belowthe reference voltage or remains unchanged. The output signal of thecomparator 222 is a pulse modulated square wave. The passive continuoustime filter 220 and the comparator 222 together convert the amplitudeinformation of an input analog signal into time information in the pulsemodulated square wave. In an embodiment, the comparator 222 may be amulti-bit comparator, resulting in multiple pulse modulated outputsignals, due to multiple levels (instead of just a high/low comparison).In the embodiment, each of the multiple pulse modulated output signalsare measured individually.

Timing properties of the comparator output signal are varied based onthe magnitude of the analog signal received at input 224 of the passivecontinuous time filter 220. Timing properties that are varied based onthe magnitude of the analog signal include the instantaneous frequencyof the comparator output signal, the duty cycle of the comparator outputsignal, or a combination of both the instantaneous frequency and theduty cycle of the comparator output signal.

In an implementation, the modulator 202 can be extended with a feedbackloop. The feedback loop routes the comparator output signal through aDigital to Analog Converter (DAC) 206, and then to the second input 226of the passive continuous time filter 220. The DAC 206 translates thecomparator output signal into an analog voltage or current signal to bereceived at the second input 226 of the passive continuous time filter220.

Measurement Engine

In an implementation, the comparator output signal is quantized by aMeasurement Engine 204 that determines the timing properties of thecontinuous time signal at the output of the comparator 222. These timingproperties describe the value of the analog input voltage atnon-equidistant time instances, i.e. irregular sampling values. Forexample, as the pulse modulated (PM) signal varies in instantaneousfrequency and duty cycle, the measurement results occur atnon-equidistant time instances. The sampling values may be quantized,and the original signal may later be reconstructed in digital form by adigital signal processor.

The Measurement Engine 204 digitally measures the edges of the modulatedsignal (which is the square wave comparator output signal), andgenerates a sample each time a data transition edge in the square waveis detected. The Measurement Engine 204 provides measurement results ofthe modulated signal at irregular intervals. In the other words, theMeasurement Engine 204 samples or measures at non-equidistant timeinstances. No clock input is needed by the Measurement Engine 204 toperform the sampling. Therefore, Measurement Engine 204 can provide highprecision sampling without a clock signal, which reduces circuitactivity of the Measurement Engine 204 and reduces power consumption ofthe PPMADC 200. Moreover, the measurement result is not corrupted bynon-idealities of the clock signal, such as jitter.

Furthermore, the Measurement Engine 204 may be used for quantization ofthe comparator output signal. For example, the Measurement Engine 204can quantize the comparator output signal into a signal with discreteinteger values or symbols. Any suitable number of binary bits can beemployed to quantize the comparator output signal. For larger bitnumbers, the number of levels that the sampled signal can be quantizedinto is larger. Therefore, the quantization noise is lower. TheMeasurement Engine 204 can be designed with digital components, such asinverters and latches, which work at higher speeds and consume loweramounts of power as compared to analog components. In an alternateimplementation, the Measurement Engine 204 may be designed using a mixof digital and analog components.

As illustrated in FIG. 2, the Measurement Engine 204 comprises a Time toDigital Converter (TDC) 210 and a control component 212. The TDC 210extracts time encoded information from the comparator output signal. Thecontrol component 212 generates stop and start events from thecomparator output signal. The generated start and stop events arenecessary for the operation of the TDC 210, including controlling thestarting and stopping of the TDC 210.

In one embodiment, the Measurement Engine 204 is comprised of a singleTDC 210 that measures both the high and the low portions of the pulsewidth encoded comparator output signal. In an alternate embodiment, theMeasurement Engine 204 is comprised of a plurality of TDCs 210. Forexample, one TDC 210 may be used to measure the high portions of thepulse width encoded comparator output signal, and another TDC 210 may beused to measure the low portions of the pulse width encoded comparatoroutput signal (since the pulse width encoded comparator output signal isa square wave). In an exemplary embodiment, any and all TDCs 210 in aPPMADC 200 are controlled solely based on the time encoded informationextracted from the comparator output signal.

FIG. 3 illustrates a circuit 300, comprising an embodiment of anexemplary PPMADC 200 with an Irregular to Regular Sample Converter(IRSC) 342 coupled to a single TDC 210 output. In an alternateembodiment, the circuit 300 may have multiple TDC 210 outputs. Forexample, one TDC 210 output may represent the instantaneous frequency ofthe encoded comparator output signal, and another TDC 210 output mayrepresent the duty cycle of the encoded comparator output signal. ThePPMADC 200 is comprised of a modulator 202 and a Measurement Engine 204.The modulator 202 is further comprised of a passive time continuousfilter 220 and a comparator 222, and may also include a DAC 206.

FIG. 3 also illustrates detail of an exemplary passive time continuousfilter 220. In the illustrated embodiment, the passive time continuousfilter 220 provides an input signal to the comparator 222. The passivetime continuous filter 220 comprises a first passive sub-filter 334, asecond passive sub-filter 336, and a summing node 338. The first passivesub-filter 334 receives an analog signal that is an input signal to thecircuit 300. As an example, the input analog signal can include voicesignals or data signals, and/or a combination of the two. In case of avoice signal, the analog source of the signal may be a microphone. Ifthe signal is a data signal, then the analog input signals may be audioand/or video transmission signals, or the like. The second passivesub-filter 336 receives a feedback signal. The feedback signaloriginates as the output signal of the comparator 222, is translated bythe DAC 206, and is fed into the second passive sub-filter 336.

As further illustrated in FIG. 3, the first and second passivesub-filters 334 and 336 are composed of passive elements, includingresistors and/or capacitors, and do not require active devices. Thefirst and second passive sub-filters 334 and 336 may be composed ofresistive elements R334 and R336 respectively, and capacitive elementsC334 and C336 respectively. Resistive elements R334 and R336 as shown inFIG. 3 may be composed of multiple passive resistors and/or passiveresistive elements. Capacitive elements C334 and C336 as shown in FIG. 3may be composed of multiple passive capacitors and/or passive capacitiveelements. An exemplary circuit showing typical resistors and capacitorsemployed as resistive elements R334 and R336 and capacitive elementsC334 and C336 respectively is illustrated below in FIG. 5.

In an exemplary embodiment, the output signal of the first passivesub-filter 334 is combined with the output signal of the second passivesub-filter 336 at the summing node 338. The output signal of the summingnode 338 is the input signal to the comparator 222. This means that theinput signal to the comparator 222 is a combination of the analog signalthat is input to the circuit 300 filtered by the first passivesub-filter 334, and the feedback signal received at the input to thesecond passive sub-filter 336 filtered by the second passive sub-filter336. Thus, the passive continuous time filter 220 directly provides aninput signal to the comparator 222.

As explained above, in one alternate embodiment, a third passivesub-filter 232 may be coupled to the output of the summing node 338. Thethird passive sub-filter 232 may passively filter the output signal ofthe summing node 338 prior to the signal being received by thecomparator 222. In one embodiment, the third passive sub-filter 222 is acapacitor (not shown) connected to the summing node 338. Thus, in allexemplary embodiments, only passive elements are in the signal pathbetween the inputs to the passive sub-filters 334 and 336 and the inputto the comparator 222.

In an exemplary embodiment, the comparator 222 compares the outputsignal of the summing node 338 and at least one reference voltage.Additionally, the comparator 222 is generally asynchronous. Timingproperties of the comparator output signal are varied based on themagnitude of the input analog signal received at the first passivesub-filter 334. Timing properties that are varied based on the magnitudeof the analog signal include the instantaneous frequency of thecomparator output signal, the duty cycle of the comparator outputsignal, or a combination of both the instantaneous frequency and theduty cycle of the comparator output signal.

In an exemplary embodiment, the DAC 206 is coupled in series between thecomparator and the second passive sub-filter 336. The DAC 206 translatesthe output signal of the comparator 222 into a voltage or current signalconfigured to be received by the second passive sub-filter 336. Thus,the output signal of the DAC 206 is the feedback signal received by thesecond passive sub-filter 336.

Demodulation

In an exemplary implementation, the comparator output signal isdigitized by a Measurement Engine 204 that provides measurement valuesof the output of the comparator 222 at non-equidistant discrete timesand generates irregular sampling values. The Measurement Engine 204 iscoupled to the output of the comparator, and extracts timing informationfrom the output signal of the comparator 222. In an implementation, theMeasurement Engine 204 extracts all control events for the extraction ofthe timing information solely from the output signal of the comparator222.

Once the Measurement Engine 204 quantizes the modulated comparatoroutput signal, the operations that follow may be purely digital. In anexemplary embodiment, a post processing circuit 340 comprising anIrregular to Regular Sample Converter (IRSC) 342 is coupled to theoutput of the Measurement Engine 204. The post processing circuit 340converts non-equidistant timing information from the output signal ofthe comparator 222 into equally spaced discrete values that representsampling values of the analog signal received by the first passivesub-filter 334. The output of the Measurement Engine 204 providesinformation regarding the original input analog signal in the measurededge positions and/or pulse width of the square wave. The input analogsignal can be reconstructed in the digital domain by the IRSC 342. TheIRSC 342 can include a demodulator (not shown). In certainimplementations, conversion of an irregular output (sampling) of theMeasurement Engine 204 to an equidistant sampling may be performed bythe demodulator.

FIG. 4 illustrates a circuit 400, comprising a differentialimplementation of an exemplary PPMADC 200 with an Irregular to RegularSample Converter (IRSC) 342 coupled to a TDC 210 output. FIG. 4 alsoillustrates detail of an exemplary passive time continuous filter 420with parallel paths for differential operation. The basic operation ofthe circuit 400 is similar to the operation of the circuit 300, butincludes fully differential signal paths. Two analog signals are inputto the first passive continuous time filter 434, and two feedbacksignals are fed to the second passive continuous time filter 436. In anembodiment, the two input analog signals may include a first inputanalog signal and a second input analog signal. In an alternateembodiment, the second input analog signal may be a reference signal.

The first input analog signal is combined with a first feedback signal,and the second input analog signal is combined with a second feedbacksignal at the summing node 438, creating a first combined signal(illustrated on signal path 460) and a second combined signal(illustrated on signal path 462). In an exemplary embodiment, the firstand second combined signals at the output of the summing node arereceived directly by the comparator 422. In an alternative embodiment,the first and second combined signals at the output of the summing nodeare filtered by a third passive time continuous filter (not shown) priorto being received by the comparator 422. The third passive timecontinuous filter may be comprised of a passive capacitive elementconnected to the first and second combined signals. Thus, in allexemplary embodiments, only passive elements are in the signal pathsbetween the inputs of the first and second passive continuous timefilters 434 and 436, and the input to the comparator 422.

In an exemplary embodiment, the comparator 422 is the only activeelement of the first stage or the second stage of the PPMADC 400.Additionally, the comparator 422 is generally asynchronous. Thecomparator 422 compares the first and second combined output signals toat least one reference signal, and outputs a pair of pulse modulatedoutput signals. Timing properties of the comparator output signals arevaried based on the magnitude of the analog signals received at thefirst and second inputs of the first passive continuous time filter 434.Timing properties that are varied based on the magnitude of the inputanalog signals include the instantaneous frequency of the comparatoroutput signals, the duty cycle of the comparator output signals, or acombination of both the instantaneous frequency and the duty cycle ofthe comparator output signals.

First and second comparator output signals (PWM square wave signals) arepassed to a Measurement Engine 404 for extraction of time encodedinformation as described above. Additionally, the first and secondcomparator output signals are translated by a DAC 406 and passed to theinputs of the second passive continuous time filter 436 as feedbacksignals. As described above, the DAC 406 translates the comparatoroutput signals into analog voltage or current signals to be received bythe second passive continuous time filter 436. In an embodiment, thefirst comparator output signal becomes the first feedback signal at thesecond passive time continuous filter 436, and the second comparatoroutput signal becomes the second feedback signal at the second passivetime continuous filter 436. In an alternate embodiment, the firstcomparator output signal becomes the second feedback signal at thesecond passive time continuous filter 436, and the second comparatoroutput signal becomes the first feedback signal at the second passivetime continuous filter 436.

FIG. 5 illustrates a circuit diagram of the passive continuous timefilter 420, the comparator 422, and the DAC 406 (shown in two parts as406A and 406B) of circuit 400 as described above with reference to FIG.4. The circuit diagram illustrates the differential inputs and pluralpaths as described above. Two analog signals VP and VN are input to thefirst passive continuous time filter 434. The first passive continuoustime filter 434 is shown in FIG. 5 as passive RC filters comprising R2,C0, and C3 and R3, C1, and C2. R2 and R3 represent passive resistiveelement R334 and C0, C1, C2, and C3 represent passive capacitive elementC334 as discussed above with reference to FIG. 3. In an embodiment, thetwo input analog signals VP and VN may include a first input analogsignal and a second input analog signal. In an alternate embodiment, thesecond input analog signal VN may be a reference signal. Two feedbacksignals Q and QN are fed to the second passive continuous time filter436. The second passive continuous time filter 436 is shown in FIG. 5 aspassive RC filters comprising R0 and C0 and R1 and C1. R0 and R1represent passive resistive element R336 and C0 and C1 represent passivecapacitive element C336 as discussed above with reference to FIG. 3.Note that the capacitors C0 and C1 are shared by both filters 434 and436 in this implementation. In alternate embodiments, the filters 434and 436 may not share common components.

The first input analog signal VP is combined with a first feedbacksignal Q at node A, and the second input analog signal VN is combinedwith a second feedback signal QN at node AN, creating a first combinedsignal D and a second combined signal DN. In the exemplary embodimentillustrated in FIG. 5, the first and second combined signals at theoutput of the summing node, D and DN, are received directly by thecomparator 422. In an alternative embodiment the first and secondcombined signals at the output of the summing node, D and DN, may befiltered by a third passive time continuous filter (not shown) prior tobeing received by the comparator 422. Thus, in all exemplaryembodiments, only passive elements are in the signal paths between theinputs of the first and second passive continuous time filters 434 and436, and the input to the comparator 422.

In the exemplary embodiment shown in FIG. 5, the comparator 422 is theonly active element of the modulator stage of the PPMADC 400. In anexemplary embodiment, the comparator 422 may be comprised of anintegrated circuit as illustrated in FIG. 5. In alternate embodiments,the comparator may be comprised of discrete electrical components, or amixture of discrete components and integrated circuits. Additionally,the comparator 422 is generally asynchronous. The comparator 422 outputsa pair of pulse modulated output signals Q and QN. The comparator 422compares the first and second combined output signals and sets itsoutput signals Q and QN depending on whether the voltage of D is greateror lesser than the voltage of DN. Timing properties of the comparatoroutput signals Q and QN are varied by the comparator 422 based on themagnitude of the analog signals VP and VN received at the first andsecond inputs of the first passive continuous time filter 434. Timingproperties that are varied based on the magnitude of the input analogsignals VP and VN include the instantaneous frequency of the comparatoroutput signals Q and QN, the duty cycle of the comparator output signalsQ and QN, or a combination of both the instantaneous frequency and theduty cycle of the comparator output signals Q and QN.

First and second comparator output signals Q and QN are passed to ameasurement engine (not shown) for extraction of time encodedinformation as described above. Additionally, the first and secondcomparator output signals Q and QN are translated by the DAC 406A and406B and passed to the inputs of the second passive continuous timefilter 436 as feedback signals. As described above, the DAC 406A and406B translates the comparator output signals Q and QN into analogvoltage or current signals to be received by the second passivecontinuous time filter 436. In an exemplary embodiment, the DAC 406A and406B may be comprised of a pair of inverters/buffers as shown in thecircuit diagram of FIG. 5. In an embodiment, the first comparator outputsignal Q becomes the first feedback signal D at the second passive timecontinuous filter 436, and the second comparator output signal QNbecomes the second feedback signal QN at the second passive timecontinuous filter 436. In an alternate embodiment, the first comparatoroutput signal Q becomes the second feedback signal DN at the secondpassive time continuous filter 436, and the second comparator outputsignal QN becomes the first feedback signal D at the second passive timecontinuous filter 436.

Exemplary Methods

FIG. 6 illustrates an exemplary method 600 for implementing analog todigital conversion using Passive Pulse Modulation Analog to DigitalConversion (PPMADC) and is described with reference to FIGS. 3-6. Theorder in which the method is described is not intended to be construedas a limitation, and any number of the described method blocks can becombined in any order to implement the method, or alternate method.Additionally, individual blocks may be deleted from the method withoutdeparting from the spirit and scope of the subject matter describedherein. Furthermore, the method can be implemented in any suitablehardware, software, firmware, or a combination thereof, withoutdeparting from the scope of the invention.

At block 602, an input analog signal is received at a first passivecontinuous time filter. The received input analog signal may includevoice signals or data signals, and/or a combination of the two. In caseof a voice signal, the analog source may be a microphone. If the signalis a data signal, then the analog input signals may be audio and/orvideo transmission signals, or the like.

At block 604, a feedback signal is received at a second passivecontinuous time filter. The feedback signal is received from a Digitalto Analog Converter (DAC). The DAC receives the feedback signal from theoutput of a comparator, and translates the comparator output signal toan analog voltage or current signal prior to sending the signal to thesecond passive continuous time filter. Block 604 may be simultaneouswith block 602, such that the input analog signal is received at thefirst passive continuous time filter simultaneous to the feedback signalbeing received at the second passive continuous time filter.

At block 606, the output signal from the first passive continuous timefilter and the output signal from the second passive continuous timefilter are combined at a summing node. In an exemplary implementation,the summing node is not comprised of an active element.

At block 608, the combined signal at the output of the summing node iscompared to at least one reference voltage at the comparator. Thecombined signal at the output of the summing node comprises the outputsignal from the first passive continuous time filter combined with theoutput signal from the second passive continuous time filter. In oneembodiment, the comparator is asynchronous. In an alternate embodiment,the comparator is synchronous. In an embodiment, the combined signal atthe output of the summing node is filtered, at a third passivecontinuous time filter, prior to being compared to at least onereference voltage at the comparator. The reference voltage can be apredefined value.

At block 610, a timing property of the output signal from the comparatoris varied based on a magnitude of the analog signal received by thefirst passive continuous time filter. In one embodiment, the timingproperty of the output signal of the comparator that is varied is theinstantaneous frequency of the output signal of the comparator. Inanother embodiment, the timing property of the output signal of thecomparator that is varied is the duty cycle of the output signal of thecomparator. In a further embodiment, the timing property of the outputsignal of the comparator that is varied is both the instantaneousfrequency of the output signal of the comparator and the duty cycle ofthe output signal of the comparator. For example, the input analogsignal may be modulated using modulator 202. The modulator 202 canconvert the magnitude (for example amplitude information) of the inputanalog signal into time information of the comparator output signalusing pulse modulation or duty cycle modulation. As a result, variationsin the amplitude of the input analog signal are converted intovariations of the pulse width and pulse period of the comparator outputsignal. The output of the modulator 202 can be an asynchronous timecontinuous square wave.

At block 612, the output signal from the comparator is measured. Themeasuring first comprises receiving the comparator output signal at aTime-to-Digital Converter (TDC). The output signal from the comparatoris also routed to a control module that is configured to control theTDC. The control module generates start and stop events for the TDCbased on the comparator output signal. Using these generated controlevents, the TDC then extracts time encoded information from thecomparator output signal.

In an alternate embodiment, a plurality of TDCs may extract the timeencoded information from the comparator output signal. For example, twoTDCs may be used to perform the extraction. A first TDC may be used toextract information relative to the varying pulse width of thecomparator output signal, and a second TDC may be used to extractinformation relative to the varying duty cycle of the comparator outputsignal. This may directly correspond to the first TDC measuring theduration of the pulse in a high state, and the second TDC measuring theduration of the low state between pulses. In an exemplary embodiment,any and all TDCs are controlled solely based on the control eventsextracted from the comparator output signal, and not from anythird-party signal.

Exemplary Electronic Device

FIG. 7 illustrates an embodiment of an electronic device 700implementing analog to digital conversion using a Passive PulseModulated Analog to Digital Converter (PPMADC). The electronic device700 can include one or more input/output interfaces 702 and DigitalSignal processor(s) DSP 704. Input/output interfaces 702 can be used toconnect input/output devices such as such as a microphone, a userscreen, a user interface (e.g., keypad, touchpad, etc.), speakers, andso on to the electronic device 700. The one or more digital signalprocessors 704 can perform control and command functions, includingaccessing and controlling the components of the electronic device 700.Digital Signal Processor(s) 704 can be a single processing unit ormultiple computing units.

The electronic device 700 can further include one or more antennae 706for transmitting and receiving radio frequency. The antennae 706 may beconfigured to receive different radio frequencies (RF) in differentbands. The antenna 706 can include smart antennas, fractal antennas,microstrip antenna, and so on.

The electronic device 700 includes an irregular sampling PPMADC 708 thatcan convert an input analog signal received via the input/outputinterfaces 702 into a digital signal. The irregular sampling analog todigital converter 708 may include Modulator 202, Measurement Engine 204and IRSC 342. In an exemplary implementation, the comparator 222 is theonly active element comprising the modulator 202.

The analog signal can first be modulated to generate asynchronous squarewaves with varying pulse width and period in accordance with theamplitude of the analog signal. This modulated signal is then measuredto generate irregular samples. The sampled signal can be quantizedbefore it is utilized to reconstruct the original signal sample bysample in digital form or a digital signal.

Demodulators 710 can be included in the electronic device 700 in orderto demodulate the signal received via the antenna, and strip off thecarried frequency to obtain a baseband digital signal representing theinput analog signal.

The baseband digital signal can be converted into an analog form.Converting to analog may be performed using a Digital to AnalogConverter (DAC) 712. Any suitable DAC 712 can be used in the electronicdevice 700. For example, Binary weighted DAC, over sampling DAC, pulsewidth modulating DAC, segmented DAC, and so on. The choice of the DAC712 may depend on the technology used, the frequency of the signal, theprecision and accuracy demanded and so on.

Amplifiers and filters 714 may also be present in the electronic device700 to amplify the signal and minimize the noise and distortion of thesignal in the useful band. The amplifiers can be power amplifiers,audio/video amplifiers, and so on. The filters in the electronic device700 can include pre filters, noise shapers, digital filters, analogfilters and so on. The electronic device 700 also includes a battery orpower supply 716 that provides power to the electronic device.

Conclusion

Although the invention has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the invention is not necessarily limited to the specific featuresor acts described. Rather, the specific features and acts are disclosedas exemplary forms of implementing the invention.

What is claimed is:
 1. An Analog to Digital Converter (ADC) electricalcircuit including an analog modulator, the analog modulator comprising:a passive continuous time filter to: receive an analog signal, toreceive a feedback signal, and to provide an output signal; and anasynchronous comparator configured to receive the output signal, thecomparator further configured to vary a timing property of an outputsignal of the comparator based on a magnitude of the analog signalreceived by the passive continuous time filter.
 2. The ADC electricalcircuit of claim 1, further comprising: a Digital to Analog Converter(DAC) coupled in series between the asynchronous comparator and thepassive continuous time filter, the DAC configured to translate theoutput signal of the comparator into a voltage or current signalconfigured to be received by the passive continuous time filter, whereinan output signal of the DAC is the feedback signal to be received by thepassive continuous time filter.
 3. The ADC electrical circuit of claim2, further comprising: a measurement engine coupled to the output of theasynchronous comparator, the measurement engine configured to extracttiming information from the output signal of the asynchronouscomparator, and to extract control events for the extraction of thetiming information from the output signal of the asynchronouscomparator.
 4. The ADC electrical circuit of claim 3, furthercomprising: a post processing circuit coupled to the measurement engine,the post processing circuit configured to convert non-equidistant timinginformation from the output signal of the asynchronous comparator intoequally spaced discrete values that represent sampling values of theanalog signal received by the passive continuous time filter.
 5. The ADCelectrical circuit of claim 1, wherein the passive continuous timefilter includes a first passive sub-filter to receive the analog signaland a second passive sub-filter to receive the feedback signal.
 6. TheADC electrical circuit of claim 1, wherein the timing property is aninstantaneous frequency of the output signal of the asynchronouscomparator.
 7. The ADC electrical circuit of claim 1, wherein the timingproperty is a duty cycle of the output signal of the asynchronouscomparator.
 8. The ADC electrical circuit of claim 1, wherein the timingproperty represents the analog signal received by the passive continuoustime filter at a sampling point within a respective cycle of the outputsignal of the comparator.
 9. The ADC electrical circuit of claim 1,wherein the passive continuous time filter includes a first passivesub-filter to receive the analog signal, a second passive sub-filter toreceive the feedback signal, and a summing node to combine outputssignals from the first and second passive sub-filters to provide theoutput signal.
 10. A method comprising: receiving an analog signal at afilter, the filter providing a first output signal; receiving a feedbacksignal from a Digital to Analog Converter (DAC) at the filter, thefilter providing a second output signal; combining the first outputsignal and the second output signal to provide a third output signal;comparing the third output signal with at least one reference voltage;and varying a timing property of a signal output by an asynchronouscomparator based on a magnitude of the analog signal received by thefilter.
 11. The method of claim 10, further comprising measuring thesignal output by the comparator by: receiving the signal output bycomparator at a Time-to-Digital Converter (TDC); and extracting timeencoded information from the signal output by the asynchronouscomparator using start and stop events based on the signal output by theasynchronous comparator.
 12. The method of claim 11, wherein thereceiving and the extracting is performed by a plurality of TDCs, andwherein the TDCs are controlled solely based on control events extractedfrom the signal output by the asynchronous comparator.
 13. The method ofclaim 10, wherein the timing property is an instantaneous frequency ofthe output signal of the asynchronous comparator.
 14. The method ofclaim 10, wherein the timing property is a duty cycle of the outputsignal of the asynchronous comparator.
 15. The method of claim 10,further comprising filtering the third output signal prior to thecomparing.
 16. An apparatus comprising: a first stage, including: afilter having at least one input and an output, the input configured toreceive an analog signal, the at least one input further configured toreceive a feedback signal, and the output configured to provide anoutput signal based on the analog signal and the feedback signal, acomparator configured to compare the output signal of the filter and atleast one reference voltage to provide a comparator output signal,wherein a timing property of the comparator output signal is variedbased on a magnitude of the analog signal received by the at least oneinput, and a Digital to Analog Converter (DAC) configured to convert thecomparator output signal into the feedback signal to be received by theat least one input; and a second stage comprising a Time-to-DigitalConverter (TDC) and a control component, the TDC configured to extracttime encoded information from the comparator output signal, and thecontrol component configured to generate start and stop events from thecomparator output signal.
 17. The apparatus of claim 16, wherein thetiming property is an instantaneous frequency of the comparator outputsignal.
 18. The apparatus of claim 16, wherein the timing property is aduty cycle of the comparator output signal.
 19. The apparatus of claim16, wherein the comparator is an asynchronous comparator.
 20. Theapparatus of claim 16, further comprising a plurality of TDCs, whereinthe TDCs are controlled solely based on the time encoded informationextracted from the comparator output signal.